Lecture # 04 Pressure Measurement Techniques and Instrumentation

Lecture # 04 Pressure Measurement Techniques and Instrumentation

AerE 344 class notes LectureLecture ## 0404 PressurePressure MeasurementMeasurement TechniquesTechniques andand InstrumentationInstrumentation Hui Hu Department of Aerospace Engineering, Iowa State University Ames, Iowa 50011, U.S.A Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! MeasurementMeasurement TechniquesTechniques forfor ThermalThermal--FluidsFluids StudiesStudies Velocity, temperature, density (concentration), etc.. • Pitot probe • hotwire, hot film Intrusive • thermocouples techniques • etc ... Thermal-Fluids measurement techniques • Laser Doppler Velocimetry (LDV) particle-based • Planar Doppler Velocimetry (PDV) techniques • Particle Image Velocimetry (PIV) • etc… Non-intrusive techniques • Laser Induced Fluorescence (LIF) • Molecular Tagging Velocimetry (MTV) molecule-based • Molecular Tagging Therometry (MTT) techniques • Pressure Sensitive Paint (PSP) • Temperature Sensitive Paint (TSP) • Quantum Dot Imaging • etc … Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! Pressure measurements • Pressure is defined as the amount of force that presses on a certain area. – The pressure on the surface will increase if you make the force on an area bigger. – Making the area smaller and keeping the force the same also increase the pressure. – Pressure is a scalar F dF P = n = n A dA nˆ dFn dA τˆ Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! Pressure measurements Pgauge = Pabsolute − Pamb Manometer Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! MechanicalMechanical PressurePressure GaugesGauges --11 Deadweight gauges: weight • High accuracy plunger plunger cylinder • Usually used for the calibration of other instruments • Application range : 102~108 pa pump •Uncertainty is within 0.01% ~0.05% of the reading Calibration pressure P Fluid chamber Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! MechanicalMechanical PressurePressure GaugesGauges --22 Elastic-element gauges: • Contain an elastic elements that deforms under pressure and creates a linear or angular displacement • The displacement is either displayed on a dial by means of purely mechanical linkages or transformed to an electric signal that can be displayed or recorder at will. • They usually used for monitoring supply pressure p p Cross sectional shape Curved Bourdon tube p Twisted Bourdon tube Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! ElectricalElectrical PressurePressure transducerstransducers • These devices provides an electric output signal that is linearly or nonlinearly dependent on the absolute pressure or a pressure difference. • They can be categorized as: – Molecular transducers: • Applied pressure or force produces a change (on the molecular level) of a electrical property of material. • Piezo-electric material such as quartz crystal: change in internal dipole moments of the molecules of the crystal when the pressure or force is applied. – Parametrical transducers: • The gross electrical parameter (resistance, inductance, capacitance) of an associate electrical parameter is altered by applied force. • Variable-capacitance transducer p E Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! WallWall PressurePressure measurementsmeasurements --11 • Making small orifice (pressure tap) facing the flow. V, P Δp = Pm − P > 0 • Machining small hole could be difficult • d = 0.5~3.0mm in practice • l/d = 5 ~ 15 is common used l P • Potential effect on the wall roughness m d • Effects of unsteady shock wave, and shock- boundary-layer interactions for transonic and supersonic flows: • PSP method to be introduced later Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! WallWall PressurePressure measurementsmeasurements -- 22 V • For a unsteady flow, the dynamic response of a pressure acquisition system is a key issue! – Dynamic response of the pressure transducers Pressure – Dynamic response of the connection tubing transducers • Remote connection – Dynamic response is low – Spatial resolution is high Connection tubing • Cavity mounting • Cavity mounting V – Dynamic response is good – Spatial resolution is high • Flush mounting – Dynamic response is high – Spatial resolution is low V pressure transducer pressure transducer Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! PressurePressure MeasurementsMeasurements insideinside FlowFlow FieldField • Non-intrusive technique is unavailable for direct pressure measurements – Based on N-S equation to calculate pressure field using the measured (PIV) velocity field. • Static probe: for static pressure measurements • Pitot probe: for total pressure measurements • Pitot-static probe: for static and total pressures measurements (velocity measurements) • Multi-hole probe: Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! PressurePressure SensitiveSensitive PaintPaint (PSP)(PSP) techniquetechnique • Composition of Air: 78.08% N2, 20.95% O2, 0.93% Ar, 0.03% CO2, 0.002% Ne, plus lesser amounts of Methane, Helium, Krypton, Hydrogen, Xenon. • The pressure of air can be determined if the particle pressure of oxygen (i.e. oxygen concentration) can be measured. • A typical pressure sensitive paint is comprised of two main parts: an oxygen sensitive fluorescent molecule and an oxygen permeable binder Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! Applications of PSP Technique PSP measurement result PSP combined with PIV Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! Applications of PSP Technique Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! PSP Technique for Low Speed Applications V∞=50m/s PSP measurements of a 2002 Ford Thunderbird Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! AerE344 Lab #03: Pressure Sensor Calibration and Measurement Uncertainty Analysis • Task #1: Pressure Sensor Calibration experiment – A pressure sensor – Setra pressure transducer with a range of +/- 5 inH2O • It has two pressure ports: one for total pressure and one for static (or reference) pressure. – A computer data acquisition system to measure the output voltage from the manometer. – A manometer of known accuracy • Mensor Digital Pressure Gage, Model 2101, Range of +/- 10 inH2O – A plenum and a hand pump to pressurize it. – Tubing to connect pressure sensors and plenum • Lab output: – Calibration curve – Repeatability of your results – Uncertainty of your measurements tubing Setra pressure Mensor Digital transducer Pressure Gage A computer A plenum hand pump (to be calibrated) Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! Calibration curves 1400 1200 y=a+bx max dev:30.4, r2=0.998 a=13.2, b=240 1000 800 600 Pressure (Pa) Pressure 400 Experimental data curve fitting 200 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Voltage (V) Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! AerE344 Lab #03: Pressure Sensor Calibration and Measurement Uncertainty Analysis • Task #2: velocity profile measurements of a Wind tunnel – A Setra manometer to be used with a Pitot- static probe. a. streamlined airfoil – A Pitot-static probe mounted to a traverse for measuring velocity profiles in the wind tunnel. – A thermometer and barometer for observing ambient lab conditions (for calculating atmospheric density). – A computer with a data acquisition system capable of measuring the voltage from your b. Flat plate pressure transducer. • Lab Output – Velocity profiles across the wind tunnel test 1 section. p = p + ρV 2 ,(Bernoulli) 0 stat 2 2( p − p ) V = 0 stat ρ Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved! Velocity profile in the Bill James wind Tunnel 12 10 8 6 Velocity (m/s) Velocity 4 2 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Position (mm) Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved!.

View Full Text

Details

  • File Type
    pdf
  • Upload Time
    -
  • Content Languages
    English
  • Upload User
    Anonymous/Not logged-in
  • File Pages
    18 Page
  • File Size
    -

Download

Channel Download Status
Express Download Enable

Copyright

We respect the copyrights and intellectual property rights of all users. All uploaded documents are either original works of the uploader or authorized works of the rightful owners.

  • Not to be reproduced or distributed without explicit permission.
  • Not used for commercial purposes outside of approved use cases.
  • Not used to infringe on the rights of the original creators.
  • If you believe any content infringes your copyright, please contact us immediately.

Support

For help with questions, suggestions, or problems, please contact us